To provide a propulsion device capable of stabilizing position of a seabed not-fixed type windmill of an offshore wind power generation facility and capable of moving in omnidirection.

The propulsion device includes a spherical propulsion source 1, having a discharge port 18 distributed evenly in a surface for discharging a propulsion water flow, a closing member 2 for rotationally moving while contacting with the surface of the spherical propulsion source and closing the discharge port at a traveling direction of the spherical propulsion source, an electromagnet 9 for attracting and fixing this closing member with the spherical propulsion source and an xy moving ring 13 and an xz face moving ring 6 for moving to optional latitude and longitude in the surface of the spherical propulsion source and the spherical propulsion source can move in every direction for 360° so that the offshore windmill becomes stabilized and movable.